IEEE 802'16

1
IEEE 802.16

D. Miorandi, CREATE-NET
2
What is WiMax

• WiMax (Worldwide Interoperability for microwave
  access)
• A technology based on an evolving standard for
  point-to-multipoint wireless networking
• The commercialization of IEEE 802.16 standard
• Solution for Wireless Metropolitan Area Network
• BWA (Broadband Wireless Access) Solution
• Comply with European BWA standard
• European Telecommunications Standards Institute's
  High-performance radio metropolitan area network
  (HiperMAN) standard

3
IEEE 802 Standard

• 802.3 CSMA/CD (Ehernet)
• 802.4 Token Bus
• 802.5 Token Ring
• 802.6 MAN
• 802.11 Wireless LAN
• 802.12 Gigabit LAN
• 802.16 Fixed Broadband Wireless Access
  System

4
802.2 Logical Link
Data Link Layer
802.1 Bridging
802.3 Medium Access 802.3 Physical
802.4 Medium Access 802.4 Physical
802.5 Medium Access 802.5 Physical
802.6 Medium Access 802.6 Physical
802.11 Medium Access 802.11 Physical
802.12 Medium Access 802.12 Physical
802.16 Medium Access 802.16 Physical
Physical Layer
The relationship between the standard and other
members of the family
5
IEEE 802.16

• 802.16 consists of the access point, BS(Base
  Station) and SSs(Subscriber Stations)
• All data traffic goes through the BS, and the BS
  can control the allocation of bandwidth on the
  radio channel.
• 802.16 is a Bandwidth on Demand system.

6
SS
SS
BS
SS
Wireless Access Network
7
IEEE 802.16

• Scope
• Specifies the air interface, MAC (Medium Access
  Control), PHY(Physical layer)
• Purpose
• to enable rapid worldwide deployment of
  cost-effective broadband wireless access products
• to facilitate competition in broadband access by
  providing alternatives to wireline broadband
  access
• Main advantage
• fast deployment, dynamic sharing of radio
  resources and low cost

8
IEEE 802.16

• IEEE 802.16 was completed on Oct, 2004
• Point-to-Multipoint (PMP) broadband wireless
  access standard for systems in the frequency
  ranges 10 66 GHz and sub 11 GHz.

9
IEEE 802.16 Extension

• 802.16a
• use the licensed and license-exempt frequencies
  from 2 to 11Ghz
• Support Mesh-Network
• 802.16b
• Increase spectrum to 5 and 6GHz
• Provide QoS (for real-time voice and video
  service)
• 802.16c
• Represents a 10 to 66GHz system profile
• 802.16d
• Improvement and fixes for 802.16a
• 802.16e
• Addresses on Mobile
• Enable high-speed signal handoffs necessary for
  communications with users moving at vehicular
  speeds

10
The family of 802.16 standard
11
The family of 802.16 standard
12
Architecture
13
PHY Considerations that Affect the MAC

• Broadband Channels
• Wide channels (20, 25, or 28 MHz)
• High capacity Downlink AND Uplink
• Multiple Access
• TDM/TDMA
• High rate burst modems
• Adaptive Burst Profiles on Uplink and Downlink
• Duplex scheme
• Time-Division Duplex (TDD)
• Frequency-Division Duplex (FDD) including Burst
  FDD
• Support for Half-Duplex Terminals

14
Protocol Architecture
Service specific convergence sublayer
MAC Common Part sublayer
Security (privacy, authentication)
TC (transmission convergence sublayer)
PHY
15
Physical Layer

• In the design of the PHY specification for 1066
  GHz, line-of-sight propagation was deemed a
  practical necessity.
• Because of the point-to-multipoint architecture,
  the BS basically transmits a TDM signal, with
  individual subscriber stations allocated time
  slots serially.
• The PHY specification defined for 1066 GHz uses
  burst single-carrier modulation with adaptive
  burst profiling in  which transmission
  parameters, including the modulation and coding
  schemes, may be adjusted individually to each
  subscriber station (SS) on a frame-by-frame
  basis. Both TDD and burst FDD variants are
  defined.
• Channel bandwidths of 20 or 25 MHz (typical U.S.
  allocation) or 28 MHz (typical European
  allocation) are specified, along with Nyquist
  square-root raised-cosine pulse shaping with a
  roll off factor of 0.25.
• NLOS operations in lower frequency bands (lt11
  GHz) are made possible by the adoption of an OFDM
  modulation scheme.

16
Transmission Convergence sublayer

• This layer performs the transformation of
  variable length MAC protocol data units (PDUs)
  into the fixed length FEC blocks (plus possibly a
  shortened block at the end) of each burst. The TC
  layer has a PDU sized to fit in the FEC block
  currently being filled. It starts with a pointer
  indicating where the next MAC PDU header starts
  within the FEC block. The TC PDU format allows
  resynchronization to the next MAC PDU in the
  event that the previous FEC block had
  irrecoverable errors.

17
Medium Access Control

• The 802.16 medium access control (MAC) layer
  supports many different physical layer
  specifications, both licensed and unlicensed.
• The 802.16 MAC is connection-oriented (!!!)

18
Service Specific Convergence Sublayer

• Supports ATM-based and IP-based networking on top
  of IEEE 802.16
• It classifies service data units (SDUs) to the
  proper MAC connection, enables QoS support,
  enable BW allocation
• May (optionally) perform header
  suppression/compression

19
Adaptive PHY

• Burst profile
• Modulation and FEC
• Dynamically assigned according to link
  conditions
• Burst by burst, per subscriber station
• Trade-off capacity vs. robustness in real time

20
Duplex Scheme Support

• On downlink, SS is associated with a specific
  burst
• On uplink, SS is allotted a variable length time
  slot for their transmissions
• Time-Division Duplex (TDD)
• Downlink Uplink time share the same RF channel
• Dynamic asymmetry
• SS does not transmit receive simultaneously
  (low cost)
• Frequency-Division Duplex (FDD)
• Downlink Uplink on separate RF channels
• Static asymmetry
• Half-duplex SSs supported
• SS does not transmit receive simultaneously
  (low cost)

21
Baud Rates Channel Size (10-66 GHz)

• Flexible plan
• allows equipment manufactures to choose according
  to spectrum requirements

QPSK 16-QAM
64-QAM
22
802.16 Frame Structure

• The FCH specifies the burst profile and the
  length of one or more DL bursts that immediately
  follow the FCH.
• A Downlink Channel Descriptor (DCD) is
  transmitted by the BS at a periodic interval to
  define the characteristics of a downlink physical
  channel.
• A Uplink Channel Descriptor (UCD) is transmitted
  by the BS at a periodic interval to define the
  characteristics of an uplink physical channel.
• Ranging Backoff Start/End
• Request Backoff Start/End
• Uplink MAP Message (UL-MAP) defines usage of the
  uplink
• contains Information Element (IE) which include
  the transmission opportunities, i.e. the time
  slots in which the SS can transmit during the
  uplink subframe
• Dowlink MAP Message (DL-MAP) defines usage of
  the downlink and contains carrier-specific data

23
Addressing and Connections

• Each SS has universal 48bit MAC address
• Connections identified by 16-bit CID
• used to distinguish between multiple uplink
  channels associated with the same downlink
  channel
• many higher-layer sessions may share same CID
  (with same service parameters)
• 3 management connections in each direction
  established automatically

24
MAC Data Frame

• The Generic MAC header has fixed format
• One or more MAC sub-headers may be part of the
  payload
• The presence of sub-headers is indicated by a
  Type field in the Generic MAC header
• The maximum length of the MAC PDU is 2048 bytes,
  including header, payload, and Cyclic Redundancy
  Check (CRC)

• Five types of sub-headers may be present.
• Fragmentation
• Grant Management
• Packing
• Mesh
• FAST-FEEDBACK allocation

25
Features

• Payload can be encrypted
• BS responsible for refreshing keying material
  periodically
• Use of CRC depends on connection ID
• CRC calculated after encryption on header
  payload
• Multiple frames may be concatenated into single
  transmission
• may join all types user data, bandwidth request
  frames and management messages
• One frame may be fragmented into several frames
• efficient use of bandwidth relative to QoS
• sequence numbers
• uses fragmentation subheader

26
More Features (Packing)

• The process of combining multiple MAC SDUs (or
  fragments thereof) into a single MAC PDU
• On connections with variable length MAC SDUs
• Packed PDU contains a sub-header for each packed
  SDU (or fragment thereof)
• On connections with fixed length MAC SDUs
• No packing sub-header needed
• Packing and fragmentation can be combined
• Can, in certain situations, save up to 10 of
  system bandwidth

27
MAC Management Messages

• Handle ranging, registration, privacy and
  describing downlink and uplink
• link describing
• BS transmits channel uplink and downlink
  descriptor messages (UCD and DCD) at periodic
  intervals
• UCD and DCD contain burst profile info on
  modulation, error-correction, preamble length,
  etc.
• uplink and downlink map messages (UL-MAP, DL-MAP)
  define burst start times and allocate access to
  corresponding link channel
• ranging subscriber stations transmit ranging
  requests at initialization and then periodically
• determines power and burst profile changes
  (starts with lowest power level and then moves
  up)

28
Management Connections

• 3 management connections correspond to 3
  different QoS levels of management traffic
• basic connection short delay
• primary management connection longer, more
  delaytolerant messages
• secondary management connection delay-tolerant,
  standards-based messages (DHCP, SNMP etc.)

29
QoS Principles

• Packets are associated with a service flow, which
  is the central concept of the MAC protocol
• Service flow an unidirectional flow of packets
  with a particular QoS
• Service flow has parameters like bandwidth,
  latency, jitter and other QoS-related variables
• When data comes to mac layer, the convergence
  sublayer gives it an connection ID (CID)
• The service flow is mapped to this ID CID,SFID

30
QoS Architecture of IEEE 802.16

• The BS determines through UL-MAP which minislots
  are subject to collision
• The BS uplink-scheduling module determines the
  IEs using bandwidth request PDU (BW-request) sent
  from SSs to BS.
• Two modes of transmitting the BW-Request
• Contention mode
• Contention-free mode (polling, piggybacking)

31
QoS Architecture of IEEE 802.16 (contd)

• In contention mode, SSs send BW-Request during
  the contention period. Contention is risolved
  using back-off
• In contention-free mode, BS polls each SS and SSs
  reply by sending BW-request.
• Due to the predictable signaling delay of the
  polling scheme, contention-free mode is suitable
  for real time applications.
• Uplink Bandwidth Allocation scheduling resides in
  the BS to control all the uplink packet
  transmissions.

32
QoS Architecture of IEEE 802.16 (contd)

• All packets from the application layer in the SS
  are classified by the Packet Classifier based on
  CID and are forwarded to the appropriate queue.
• At the SS, the scheduler will retrieve the
  packets from the queues and transmit them to the
  network in the appropriate time slots as defined
  by the UL-MAP sent by the BS.
• The UL-MAP is determined by the Uplink Bandwidth
  Allocation Scheduling based on the BW-Request
  messages that report the current queue size of
  each connection in SS.
• For UGS, BW-Request is not required.
• For rtPS, nrtPS and BE, the current queue size
  is included in the BW-request to represent the
  current bandwidth demand
• In summary, IEEE 802.16 defines
• The signaling mechanism for information exchange
  between BS and SS such as the connection setup,
  BW-Request, and UL-MAP
• The Uplink Scheduling for UGS service flow
• IEEE 802.16 does not define
• The Uplink scheduling for rtPS, nrtPS, BE service
  flow
• The Admission Control and Traffic Policing
  process

33
QoS Architecture of IEEE 802.16 (contd)
34
Table 1 End-user Performance Expectations
Conversational/Real-time Services
35
Table 2 End-user Performance Expectations
Interactive Services
36
Table 3 End-user Performance Expectations
Streaming Services
37
Binary Exponential Backoff (BEB)

• The BS schedules one RIE per uplink frame
  through a UL-MAP message
• Each RIE consist of a number of Contention
  Opportinities (CO) for contention based random
  access
• BS-controlled BEB with a minimum backoff window
  (BW) and a maximum BW
• BW values are power-of-two and are specified as
  part of UCD message (a value of 3 indicates a
  window between 0 and 7)
• When an SS has bandwidth request and wants to
  access the channel, it sets its internal BW to
  BWmin defined in the UCD message of UL-MAP
  message currently in effect. Then the SS shall
  randomly select a number within its BW.
• This random value indicates the number of COs
  that the SS shall defer befor trasmitting

38
QoS Provisioning
39
Request/Grant Scheme

• Increasing (or decreasing) bandwidth requirements
  is necessary for all services except
  incompressible constant bit rate UGS connections.
• The needs of incompressible UGS connections do
  not change between connection establishment and
  termination.
• The requirements of compressible UGS connections,
  such as channelized T1, may increase or decrease
  depending on traffic.
• 802.16 emplys a self-correcting mechanism for BW
  request/grant
• No acknowledgements
• All errors are handled in the same way, i.e.,
  periodical aggregate requests
• The period may be a function of the QoS of a
  particular service and of the link quality
• Bandwidth Requests are always per Connection
• Grants are either per Connection (GPC) or per
  Subscriber Station (GPSS)
• Grants (given as durations) are carried in the
  UL-MAP messages
• SS needs to convert the time to amount of data
  using information about the UIUC

40
Bandwidth Request Header

• Bandwidth is always requested on a CID basis and
  bandwidth is allocated on a SS basis
• The Bandwidth Request PDU consist of bandwidth
  request header alone and not contain a payload.
• Come from the Connection
• Several kinds of requests
• Implicit requests (UGS)
• No actual messages, negotiated at connection
  setup
• BW request messages
• Uses the special BW request header
• Requests up to 32 KB with a single message
• Incremental or aggregate, as indicated by MAC
  header
• Piggybacked request (for non-UGS services only)
• Presented in GM sub-header and always incremental
• Up to 32 KB per request for the CID
• Poll-Me bit (for UGS services only)
• Used by the SS to request a bandwidth poll for
  non-UGS services

41
GPSS vs. GPCC

• Two basic approaches on the way to grant BW
• Bandwidth Grant per Subscriber Station (GPSS)
• Base station grants bandwidth to the subscriber
  station
• Subscriber station may re-distribute bandwidth
  among its connections, maintaining QoS and
  service-level connections agreements
• Suitable for many connections per terminal
  off-loading base stations work
• Allows more sophisticated reaction to QoS needs
• Low overhead but requires intelligent subscriber
  station
• Mandatory for P802.16 10-66 GHz PHY
• Bandwidth Grant per Connection (GPC)
• Base station grants bandwidth to a connection
• Mostly suitable for few users per subscriber
  station
• Higher overhead, but allows simpler subscriber

42
Maintaining QoS in GPSS

• Semi-distributed approach
• BS sees the requests for each connection based
  on this, grants bandwidth (BW) to the SSs
  (maintaining QoS and fairness)
• SS scheduler maintains QoS among its connections
  and is responsible to share the BW among the
  connections (maintaining QoS and fairness)
• Algorithm in BS and SS can be very different SS
  may use BW in a way unforeseen by the BS

43
Network Entry

• In order to communicate on the network an SS
  needs to successfully complete the network entry
  process with the desired BS.
• The network entry process is divided into
• DL channel synchronization
• Initial ranging
• Capabilities negotiation
• Authentication message exchange
• Registration
• IP connectivity
• The network entry state machine moves to reset
  if it fails to succeed from a state.
• Upon completion of the network entry process,
  the SS creates one or more service flows to send
  data to the BS.

44
Downlink Channel Synchronization

• When an SS wishes to enter the network, it scans
  for a channel in the defined frequency list.
• Normally an SS is configured to use a specific BS
  with a given set of operational parameters, when
  operating in a licensed band.
• If the SS finds a DL channel and is able to
  synchronize at the PHY level (it detects the
  periodic frame preamble)
• The MAC layer looks for DCD and UCD to get
  information on modulation and other DL and UL
  parameters.

45
Initial Ranging

• When an SS has synchronized with the DL channel
  and received the DL and UL MAP for a frame, it
  begins the initial ranging process by sending a
  ranging request MAC message on the initial
  ranging interval using the minimum transmission
  power.
• If it does not receive a response
• The SS sends the ranging request again in a
  subsequent frame, using higher transmission
  power.
• Eventually the SS receives a ranging response.
• The response either indicates power and timing
  corrections that the SS must make or indicates
  success.
• If the response indicates corrections,
• the SS makes these corrections and sends another
  ranging request.
• If the response indicates success,
• the SS is ready to send data on the UL.

46
Negotiation Capabilities

• After successful completion of initial ranging,
  the SS sends a capability request message to the
  BS describing its capabilities in terms of the
  supported modulation levels, coding schemes and
  rates, and duplexing methods.
• The BS accepts or denies the SS, based on its
  capabilities.

Authentication

• After capability negotiation, the BS
  authenticates the SS and provides key material to
  enable the ciphering of data.
• The SS sends the X.509 certificate of the SS
  manufacturer and a description of the supported
  cryptographic algorithms to its BS.
• The BS validates the identity of the SS,
  determines the cipher algorithm and protocol that
  should be used, and sends an authentication
  response to the SS.
• The response contains the key material to be used
  by the SS.
• The SS is required to periodically perform the
  authentication and key exchange procedures to
  refresh its key material.

47
Registration

• After successful completion of authentication the
  SS registers with the network.
• The SS sends a registration request message to
  the BS, and the BS sends a registration response
  to the SS.
• The registration exchange includes
• IP version support
• SS managed or non-managed support
• ARQ parameters support
• Classification option support
• CRC support
• Flow Control

IP Connectivity

• The SS then starts DHCP (IETF RFC 2131) to get
  the IP address and other parameters to establish
  IP connectivity
• The BS and SS maintain the current date and time
  using the time of the day protocol (IETF RFC868).
  The SS then downloads operational parameters
  using TFTP (IETF RFC 1350).

48
Transport Connection Creation

• After completion of registration and the transfer
  of operational parameters, transport connections
  are created.
• For preprovisioned service flows, the connection
  creation process is initiated by the BS.
• The BS sends a dynamic service flow addition
  request message to the SS and the SS sends a
  response to confirm the creation of the
  connection.
• Connection creation for non-preprovisioned
  service flows is initiated by the SS by sending a
  dynamic service flow addition request message to
  the BS.
• The BS responds with a confirmation.

49
Acknowledgments

• A special thank to N. Scalabrino for having
  provided some (?) base material

50
Downlink/Uplink Scheduling

• Radio resources have to be scheduled according to
  the QoS(Quality of Service) parameters
• Downlink scheduling
• the flows are simply multiplexed
• the standard scheduling algorithms can be used
• WRR(Weighted Round Robin)
• VT(Virtual Time)
• WFQ(Weighted Fair Queueing)
• WFFQ(Worst-case Fair weighted Fair Queueing)
• DRR(Deficit Round Robin)
• DDRR(Distributed Deficit Round Robin)

51
WRR

• It is an extention of round robin scheduling

based on the static weight.
Counter Reset Cycle
1
1
1
VCC 1 (Source 1)
2
1
1
2
3
1
1
1
2
3
3
3
3
3
2
2
VCC 2 (Source 2)
3
WRR scheduler
3
3
3
VCC 3 (Source 3)
3
3
52
VT

• VT aims to emulate the TDM(Time Division
  Multiplexing) system
• connection 1 reserves 50 of the link bandwidth
• connection 2, 3 reserves 20 of the link
  bandwidth

Connection 1 Average
inter-arrival 2 units
Connection 1 Average
inter-arrival 2 units
Connection 2 Average
inter-arrival 5 units
Connection 3 Average
inter-arrival 5 units
First-Come-First-Served service order
Virtual times
Virtual Clock service order
53
FFQ

• FFQ(Fluid Fair Queue) head-of-the line
  processor sharing service discipline
• guaranteed rate to connection i
• C the link speed
• the set of non-empty queue
• The service rate for a non-empty queue i

54
WFQ and WFFQ

• WFQ picks the first packet that would complete
  service in the corresponding FFQ system
• WFFQ picks the first packet that would complete
  service among the set of packets that have
  started service in the corresponding FFQ system

55
VT and WFQ

• All packets are fixed size and require exactly
  one second to service
• Starting at time zero, 1000 packets from
  connection 1 arrive at a rate of 1 packet/second
• Starting at time 900, 450 packets from connection
  2 arrive at a rate of 1 packet/second
• The completion times of the 901, 902, 903,
  packets of connection 1 in FFQ system are 1802,
  1904, 1806,
• The completion times of the 1, 2, 3, packets of
  connection 2 in FFQ system are 901, 902, 903,

56

Connection 1
Connection 1
Connection 2
Virtual Clock Service Order
898
900
902
904
WFQ Service Order
898
900
902
904
Figure 7. WFQ and Virtual Clock
57
Deficit Round Robin

• Each connection is assigned a state variable
  called the DC(Deficit Counter).
• At the start of each round, DCi of queue i is
  incremented by a specific service share(quantum)
• If the length of the head of the line packet, Li,
  is less than or equal to DCi,, the scheduler
  allows the ith queue to send a packet.
• Once the transmission is completed DCi is
  decremented by Li.

58

• Deficit Round Robin Scheme

Qi
3500
initializing
(1st round)
DCi
3500
2800
7800
2000
serviced
1500
2800
7800
2000
Not serviced
(2nd round)
5000
2800
7800
2000
serviced
(3rd round)
700
2800
7800
2000
serviced
(4th round)
1400
2800
7800
2000
59
Distributed Deficit Round Robin

• Each connection is assigned a state variable
  called the DC(Deficit Counter)
• If the value of the DCi is positive then the
  scheduler allows the ith queue to send a packet.
• Once the transmission is completed DCi is
  decremented by Li, the length of the transmitted
  packet .
• At the start of the subsequent rounds, DCi is
  incremented by a specific service share(quantum)

60

• Distributed Deficit Round Robin Scheme

Qi
3500
initializing
(1st round)
DCi
3500
2800
7800
2000
serviced
1500
2800
7800
2000
serviced
-6300
2800
7800
2000
Not serviced
(2nd round)
-2800
2800
7800
2000
Not serviced
700
2800
7800
2000
(3rd round)
serviced
-2100
2800
7800
2000
61
Downlink/Uplink Scheduling

• Uplink scheduling
• Responsible for the efficient and fair allocation
  of the resources(time slots) in the uplink
  direction
• Uplink carrier
• Reserved slots
• contention slots(random access slots)
• The standard scheduling algorithms can be used